GH-37978: [C++] Add support for specifying custom Array element delimiter to arrow::PrettyPrintOptions

cpp/src/arrow/pretty_print.cc

@@ -151,22 +151,22 @@ class ArrayPrinter : public PrettyPrinter {
         IndentAfterNewline();
         (*sink_) << "...";
         if (!is_last && options_.skip_new_lines) {
-          (*sink_) << ",";
+          (*sink_) << options_.array_delimiters.element;
         }
         i = array.length() - window - 1;
       } else if (array.IsNull(i)) {
         IndentAfterNewline();
         (*sink_) << options_.null_rep;
         if (!is_last) {
-          (*sink_) << ",";
+          (*sink_) << options_.array_delimiters.element;
         }
       } else {
         if (indent_non_null_values) {
           IndentAfterNewline();
         }
         RETURN_NOT_OK(func(i));
         if (!is_last) {
-          (*sink_) << ",";
+          (*sink_) << options_.array_delimiters.element;
         }
       }
       Newline();
@@ -453,12 +453,12 @@ Status PrettyPrint(const ChunkedArray& chunked_arr, const PrettyPrintOptions& op
   if (!skip_new_lines) {
     *sink << "\n";
   }
-  bool skip_comma = true;
+  bool skip_element_delimiter = true;
   for (int i = 0; i < num_chunks; ++i) {
-    if (skip_comma) {
-      skip_comma = false;
+    if (skip_element_delimiter) {
+      skip_element_delimiter = false;
     } else {
-      (*sink) << ",";
+      (*sink) << options.chunked_array_delimiters.element;
       if (!skip_new_lines) {
         *sink << "\n";
       }
@@ -467,12 +467,13 @@ Status PrettyPrint(const ChunkedArray& chunked_arr, const PrettyPrintOptions& op
       for (int i = 0; i < indent; ++i) {
         (*sink) << " ";
       }
-      (*sink) << "...,";
+      (*sink) << "...";
+      (*sink) << options.chunked_array_delimiters.element;
       if (!skip_new_lines) {
         *sink << "\n";
       }
       i = num_chunks - window - 1;
-      skip_comma = true;
+      skip_element_delimiter = true;
     } else {
       PrettyPrintOptions chunk_options = options;
       chunk_options.indent += options.indent_size;

cpp/src/arrow/pretty_print.h

@@ -32,7 +32,21 @@ class Schema;
 class Status;
 class Table;
 
-struct PrettyPrintOptions {
+/// \class PrettyPrintDelimiters
+/// \brief Options for controlling which delimiters to use when printing
+/// an Array or ChunkedArray.
+struct ARROW_EXPORT PrettyPrintDelimiters {
+  /// Delimiter for separating individual elements of an Array (e.g. ","),
+  /// or individual chunks of a ChunkedArray
+  std::string element = ",";
+
+  /// Create a PrettyPrintDelimiters instance with default values
+  static PrettyPrintDelimiters Defaults() { return PrettyPrintDelimiters(); }
+};
+
+/// \class PrettyPrintOptions
+/// \brief Options for controlling how various Arrow types should be printed.
+struct ARROW_EXPORT PrettyPrintOptions {
   PrettyPrintOptions() = default;
 
   PrettyPrintOptions(int indent,  // NOLINT runtime/explicit
@@ -47,6 +61,7 @@ struct PrettyPrintOptions {
         skip_new_lines(skip_new_lines),
         truncate_metadata(truncate_metadata) {}
 
+  /// Create a PrettyPrintOptions instance with default values
   static PrettyPrintOptions Defaults() { return PrettyPrintOptions(); }
 
   /// Number of spaces to shift entire formatted object to the right
@@ -77,6 +92,12 @@ struct PrettyPrintOptions {
 
   /// If true, display schema metadata when pretty-printing a Schema
   bool show_schema_metadata = true;
+
+  /// Delimiters to use when printing an Array
+  PrettyPrintDelimiters array_delimiters = PrettyPrintDelimiters::Defaults();
+
+  /// Delimiters to use when printing a ChunkedArray
+  PrettyPrintDelimiters chunked_array_delimiters = PrettyPrintDelimiters::Defaults();
 };
 
 /// \brief Print human-readable representation of RecordBatch

cpp/src/arrow/pretty_print_test.cc

@@ -200,6 +200,65 @@ TEST_F(TestPrettyPrint, PrimitiveTypeNoNewlines) {
   CheckPrimitive<Int32Type, int32_t>(options, is_valid, values, expected, false);
 }
 
+TEST_F(TestPrettyPrint, ArrayCustomElementDelimiter) {
+  PrettyPrintOptions options{};
+  // Use a custom array element delimiter of " | ",
+  // rather than the default delimiter (i.e. ",").
+  options.array_delimiters.element = " | ";
+
+  // Short array without ellipsis
+  {
+    std::vector<bool> is_valid = {true, true, false, true, false};
+    std::vector<int32_t> values = {1, 2, 3, 4, 5};
+    static const char* expected = R"expected([
+  1 | 
+  2 | 
+  null | 
+  4 | 
+  null
+])expected";
+    CheckPrimitive<Int32Type, int32_t>(options, is_valid, values, expected, false);
+  }
+
+  // Longer array with ellipsis
+  {
+    std::vector<bool> is_valid = {true, false, true};
+    std::vector<int32_t> values = {1, 2, 3};
+    // Append 20 copies of the value "10" to the end of the values vector.
+    values.insert(values.end(), 20, 10);
+    // Append 20 copies of the value "true" to the end of the validity bitmap vector.
+    is_valid.insert(is_valid.end(), 20, true);
+    // Append the values 4, 5, and 6 to the end of the values vector.
+    values.insert(values.end(), {4, 5, 6});
+    // Append the values true, false, and true to the end of the validity bitmap vector.
+    is_valid.insert(is_valid.end(), {true, false, true});
+    static const char* expected = R"expected([
+  1 | 
+  null | 
+  3 | 
+  10 | 
+  10 | 
+  10 | 
+  10 | 
+  10 | 
+  10 | 
+  10 | 
+  ...
+  10 | 
+  10 | 
+  10 | 
+  10 | 
+  10 | 
+  10 | 
+  10 | 
+  4 | 
+  null | 
+  6
+])expected";
+    CheckPrimitive<Int32Type, int32_t>(options, is_valid, values, expected, false);
+  }
+}
+
 TEST_F(TestPrettyPrint, Int8) {
   static const char* expected = R"expected([
   0,
@@ -1020,6 +1079,58 @@ TEST_F(TestPrettyPrint, ChunkedArrayPrimitiveType) {
   CheckStream(chunked_array_2, {0}, expected_2);
 }
 
+TEST_F(TestPrettyPrint, ChunkedArrayCustomElementDelimiter) {
+  PrettyPrintOptions options{};
+  // Use a custom ChunkedArray element delimiter of ";",
+  // rather than the default delimiter (i.e. ",").
+  options.chunked_array_delimiters.element = ";";
+  // Use a custom Array element delimiter of " | ",
+  // rather than the default delimiter (i.e. ",").
+  options.array_delimiters.element = " | ";
+
+  const auto chunk = ArrayFromJSON(int32(), "[1, 2, null, 4, null]");
+
+  // ChunkedArray with 1 chunk
+  {
+    const ChunkedArray chunked_array(chunk);
+
+    static const char* expected = R"expected([
+  [
+    1 | 
+    2 | 
+    null | 
+    4 | 
+    null
+  ]
+])expected";
+    CheckStream(chunked_array, options, expected);
+  }
+
+  // ChunkedArray with 2 chunks
+  {
+    const ChunkedArray chunked_array({chunk, chunk});
+
+    static const char* expected = R"expected([
+  [
+    1 | 
+    2 | 
+    null | 
+    4 | 
+    null
+  ];
+  [
+    1 | 
+    2 | 
+    null | 
+    4 | 
+    null
+  ]
+])expected";
+
+    CheckStream(chunked_array, options, expected);
+  }
+}
+
 TEST_F(TestPrettyPrint, TablePrimitive) {
   std::shared_ptr<Field> int_field = field("column", int32());
   auto array = ArrayFromJSON(int_field->type(), "[0, 1, null, 3, null]");